Medical fluid pump systems and related components and methods

ABSTRACT

A medical fluid delivery cassette configured for use with a medical fluid pumping system. The cassette includes a base, a membrane attached to the base, and an adhesive disposed on a portion of the membrane overlying a fluid pump chamber of the cassette. The portion of the membrane overlying the fluid pump chamber is moveable such that the volume of the fluid pump chamber can be changed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.12/725,673, now U.S. Pat. No. 8,192,401 filed on Mar. 17, 2010, whichclaims the benefit under 35 U.S.C. §119(e) of U.S. Application Ser. No.61/162,134, filed on Mar. 20, 2009. The above-referenced applicationsare incorporated by reference herein.

TECHNICAL FIELD

This disclosure relates to medical fluid pump systems and relatedcomponents and methods.

BACKGROUND

Dialysis is a treatment used to support a patient with insufficientrenal function. The two principal dialysis methods are hemodialysis andperitoneal dialysis.

During hemodialysis (“HD”), the patient's blood is passed through adialyzer of a dialysis machine while also passing a dialysis solution ordialysate through the dialyzer. A semi-permeable membrane in thedialyzer separates the blood from the dialysate within the dialyzer andallows diffusion and osmosis exchanges to take place between thedialysate and the blood stream. These exchanges across the membraneresult in the removal of waste products, including solutes like urea andcreatinine, from the blood. These exchanges also regulate the levels ofother substances, such as sodium and water, in the blood. In this way,the dialysis machine acts as an artificial kidney for cleansing theblood.

During peritoneal dialysis (“PD”), the patient's peritoneal cavity isperiodically infused with sterile aqueous solution, referred to as PDsolution or dialysate. The membranous lining of the patient's peritoneumacts as a natural semi-permeable membrane that allows diffusion andosmosis exchanges to take place between the solution and the bloodstream. These exchanges across the patient's peritoneum result in theremoval waste products, including solutes like urea and creatinine, fromthe blood, and regulate the levels of other substances, such as sodiumand water, in the blood.

Many PD machines are designed to automatically infuse, dwell, and draindialysate to and from the patient's peritoneal cavity. The treatmenttypically lasts for several hours, often beginning with an initial draincycle to empty the peritoneal cavity of used or spent dialysate. Thesequence then proceeds through the succession of fill, dwell, and drainphases that follow one after the other. Each phase is called a cycle.

SUMMARY

In one aspect of the invention, a medical fluid pump system includes amovable piston head and a cassette. The cassette includes a basedefining an opening and a membrane attached to the base covering theopening. The membrane together with the base define a fluid pumpchamber, a flow pathway that leads from the fluid pump chamber to aninlet of the cassette, and a flow pathway that leads from the fluid pumpchamber to an outlet of the cassette. The cassette is positioned so thatthe membrane faces the piston head and can be moved by the piston headto change a volume of the fluid pump chamber. An adhesive is disposedbetween and in contact with the piston head and the membrane. Theadhesive has sufficient affinity for the piston head to allow the pistonhead to retract and deflect the membrane outward to increase the volumeof the fluid pump chamber while maintaining adhesive contact with themembrane. The adhesive has substantially greater affinity for themembrane than for the piston head such that the piston head can beretracted in a manner to separate the piston head from the adhesivewithout separating the adhesive from the membrane.

In another aspect of the invention, a medical fluid delivery cassetteincludes a base defining an opening and a membrane attached to the basecovering the opening. The membrane together with the base define a fluidpump chamber, a flow pathway that leads from the fluid pump chamber toan inlet of the cassette, and a flow pathway that leads from the fluidpump chamber to an outlet of the cassette. A portion of the membraneoverlying the fluid pump chamber is moveable relative to the base suchthat the volume of the fluid pump chamber can be changed by applying aforce to the portion of the membrane overlying the fluid pump chamber.An adhesive coating is disposed on an outside surface of the portion ofthe membrane overlying the fluid pump chamber, and a release layersubstantially covers and is releasably attached to the adhesive coating.

In an additional aspect of the invention, a medical fluid deliverymethod includes adhering a first piston head of a medical system to amembrane of a medical fluid delivery cassette by moving the first pistonhead into contact with adhesive disposed on a portion the membraneoverlying a first fluid pump chamber, and, with the first piston headadhered to the membrane, changing a volume of the first fluid pumpchamber by flexing the portion of the membrane overlying the first fluidpump chamber with the first piston head.

Implementations can include one or more of the following features.

In some implementations, the piston head is adapted to be moved awayfrom the cassette with a force sufficient to overcome the affinitybetween the piston head and the adhesive such that the piston head canbe separated from the membrane.

In certain implementations, the piston head is arranged to be moved adistance of at least 1.5 centimeters away from a plane in which themembrane lies when the membrane is not deformed by the piston head.

In some implementations, the system includes a wall adjacent thecassette, and the piston head can be retracted beyond an outer surfaceof the wall.

In certain implementations, the piston head includes (e.g., is formedof) polyoxymethylene and the membrane includes (e.g., is formed of) alow density polyolefin.

In some implementations, the adhesive includes (e.g., is formed of)synthetic rubber (e.g., a double coated synthetic rubber tape).

In certain implementations, an adhesion strength of the adhesive topolyester is about 89 Oz./in. (about 97 N/100 mm), as tested using theASTM D3330 test (90 degree, 2 mil Al foil, 72 hour RT).

In some implementations, an adhesion strength of the adhesive topolypropylene is about 85 Oz./in. (about 93 N/100 mm), as tested usingthe ASTM D3330 test (90 degree, 2 mil Al foil, 72 hour RT).

In certain implementations, an adhesion strength of the adhesive topolycarbonate is about 101 Oz./in. (about 110 N/100 mm), as tested usingthe ASTM D3330 test (90 degree, 2 mil Al foil, 72 hour RT).

In some implementations, an adhesion strength of the adhesive 161 tostainless steel is about 97 Oz./in. (about 106 N/100 mm), as testedusing the ASTM D3330 test (90 degree, 2 mil Al foil, 72 hour RT).

In certain implementations, an adhesion strength of the adhesive to themembrane is substantially greater than an adhesion strength of theadhesive to the piston head.

In some implementations, the adhesive includes a first layer of adhesivein contact with the membrane and a second layer of adhesive in contactwith the piston head.

In certain implementations, the medical fluid pump system furtherincludes a base layer (e.g., a substantially liquid impermeable baselayer) disposed between the first and second layers of adhesive.

In some implementations, the first layer of adhesive is biocompatibleand the second layer of adhesive is bioincompatible.

In certain implementations, the piston head is movable in a directionsubstantially perpendicular to the cassette.

In some implementations, the piston head can be separated from theadhesive by moving the piston head in the direction substantiallyperpendicular to the cassette.

In certain implementations, the piston head is configured to be rotatedrelative to the cassette.

In some implementations, the piston head can be separated from theadhesive by rotating the piston head relative to the cassette.

In certain implementations, the base of the cassette is a moldedtray-like base.

In some implementations, the adhesive is disposed on a portion of themembrane overlying the fluid pump chamber.

In certain implementations, the adhesive is substantially uniformlydisposed on the portion of the membrane overlying the fluid pumpchamber.

In some implementations, the medical system includes first and secondmovable piston heads, and the membrane together with the base definesfirst and second fluid pump chambers, flow pathways that lead from thefirst and second fluid pump chambers to the inlet of the cassette, andflow pathways that lead from the first and second fluid pump chambers tothe outlet of the cassette. The cassette is positioned so that themembrane faces the first and second piston heads and can be moved by thefirst and second piston heads to alter volumes of the first and secondfluid pump chambers, and adhesive is disposed between and in contactwith the first and second piston heads and the membrane. The adhesivehas sufficient affinity for the first and second piston heads to allowthe first and second piston heads to retract and deflect the membraneoutward to increase the volumes of the first and second fluid pumpchambers while maintaining adhesive contact with the membrane. Theadhesive has substantially greater affinity for the membrane than forthe first and second piston heads such that the first and second pistonheads can be retracted in a manner to separate the first and secondpiston heads from the adhesive without separating the adhesive from themembrane.

In certain implementations, the medical fluid pump system is a dialysissystem (e.g., a peritoneal dialysis system).

In some implementations, the adhesive coating is produced by applyingthe release layer carrying adhesive to the membrane.

In certain implementations, the release layer is release paper (e.g., awax-coated paper).

In some implementations, the adhesive coating is disposed on a portionof the membrane that is contacted by a piston head of a medical fluidpump system during use.

In certain implementations, the release layer is removable from theadhesive coating to expose at least a portion of the adhesive coating.

In some implementations, the release layer includes a pull tab thatextends beyond an outer boundary of the adhesive.

In certain implementations, the membrane includes a low densitypolyolefin.

In some implementations, the medical fluid delivery cassette isconfigured for use with a dialysis machine (e.g., a peritoneal dialysismachine).

In certain implementations, the medical fluid delivery cassette isdisposable.

In some implementations, the adhesive coating has a greater affinity forthe membrane than for a piston head of a medical fluid pumping systemwhen the cassette is in use with the medical fluid pumping system suchthat the piston head can be retracted in a manner to separate the pistonhead from the adhesive without separating the adhesive from themembrane.

In certain implementations, the adhesive coating includes first andsecond layers of adhesive, and the first layer of adhesive is in contactwith the membrane.

In some implementations, the adhesive has a greater affinity for themembrane than for the first piston head such that the first piston headcan be retracted in a manner to separate the first piston head from theadhesive without separating the adhesive from the membrane.

In certain implementations, flexing the portion of the membraneoverlying the first fluid pump chamber includes moving the first pistonhead away from the cassette with a force that does not exceed theaffinity between the membrane and the adhesive.

In some implementations, the medical fluid delivery method furtherincludes decoupling the first piston head from the membrane by movingthe first piston head relative to the cassette.

In certain implementations, the adhesive remains attached to themembrane after decoupling the first piston head from the membrane.

In some implementations, the medical fluid delivery method furtherincludes decoupling the first piston head from the membrane by movingthe piston head in a direction substantially perpendicular to thecassette.

In certain implementations, the medical fluid delivery method furtherincludes decoupling the first piston head from the membrane by rotatingthe piston head relative to the cassette.

In some implementations, the medical fluid delivery method furtherincludes adhering a second piston head to the membrane by moving thesecond piston head into contact with adhesive disposed on a portion ofthe membrane overlying a second fluid pump chamber and, with the secondpiston head adhered to the membrane, changing a volume of the secondfluid pump chamber by flexing the portion of the membrane overlying thesecond fluid pump chamber with the second piston head.

In certain implementations, the medical fluid delivery method furtherincludes disposing the adhesive on the membrane by applying a releaselayer carrying adhesive to the membrane.

In some implementations, the medical fluid delivery method furtherincludes removing the release layer from the adhesive.

In certain implementations, removing the release layer includes pullingon a pull tab of the release paper, where the pull tab extends beyond anouter boundary of the adhesive prior to removing the release layer fromthe adhesive.

Implementations can include one or more of the following advantages.

In some implementations, the PD system includes an adhesive disposedbetween the piston head and the membrane. This arrangement permits thepiston head to be moved in a direction away from the cassette to drawdialysate into the cassette without extensive use of a vacuum system.For example, while the PD system may include a vacuum system to deflateinflatable valves that are used to direct fluid through desired pathwaysof the cassette, the membrane of the cassette in the region of the pumpchamber can be attached to the piston head using only adhesive. By usingadhesive, as opposed to vacuum pressure, to secure the membrane of thecassette to the piston head, the likelihood of fluid being pulledthrough the membrane (e.g., through very small holes in the membrane) issubstantially reduced or eliminated. Additionally or alternatively, thelevel of noise produced by the PD system during operation can besubstantially reduced relative to certain prior PD systems that usevacuum pressure retract the cassette membrane in the region of the pumpchamber as the piston head is retracted. In addition, the use ofadhesive to secure the membrane of the cassette to the piston head canreduce the overall cost and complexity of manufacturing the PD system.

In certain implementations, the piston head is adhesively attached tothe membrane of the cassette and can draw the membrane away from thecassette to draw dialysate into the cassette. The adhesive attachmentbetween the piston head and the membrane can result in a substantiallydirect correlation between the piston head position and the volume drawninto the cassette. Thus, adhesively attaching the piston head to themembrane can improve the speed and accuracy of volumetric calculationsof dialysate drawn into the cassette. Additionally or alternatively, ifany holes (e.g., pinholes) were to develop in the portion of themembrane to which the adhesive is attached, the adhesive could act as aseal and thus reduce the likelihood that fluid will leak out of thecassette.

In certain implementations, the adhesion strength or affinity of theadhesive to the membrane of the cassette is greater than the adhesionstrength or affinity of the adhesive to the piston head. In such aconfiguration, the piston head can be moved away from the membrane by asufficient distance and with a sufficient force to detach the pistonhead from the adhesive without detaching the adhesive from the membrane.The piston head can, for example, be retracted with a force greater thanthe adhesion strength of the adhesive to the piston head but less thanthe adhesion strength of the adhesive to the membrane of the cassette todetach the piston head from the adhesive while retaining the attachmentbetween the adhesive and the membrane of the cassette. The particularmaterial properties of the adhesive, cassette membrane, and piston headinhibit or eliminate adhesive from remaining attached to the piston headupon detachment of the piston head from the membrane and can thus reduceor prevent adhesive build-up in the PD system over time.

In some implementations, the cassette is disposable. In suchimplementations, the cassette, along with adhesive retained on thecassette, can be discarded after use. Such a disposable cassette canreduce the need for the user to remove or otherwise handle the adhesive.

In certain implementations, a release layer (e.g., a release paper)covers and is releasably attached to adhesive on the cassette. Therelease layer can be removed to expose the adhesive before use. Therelease layer can help to prevent debris and contaminants fromcollecting on the adhesive prior to use of the cassette.

Other aspects, features, and advantages will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a PD system.

FIG. 2 is a perspective view of a PD cycler and PD cassette of the PDsystem of FIG. 1. A door of the PD cycler is in the open position toshow the inner surfaces of the PD cycler that interface with the PDcassette during use.

FIG. 3 is a perspective view of a cassette compartment of the PD cyclerof FIGS. 1 and 2.

FIG. 4 is a perspective view from a rigid base side of the PD cassetteof the PD system of FIG. 1.

FIG. 5 is a perspective view from a flexible membrane side of the PDcassette of the PD system of FIG. 1.

FIG. 6 is a plan view from the membrane side of the PD cassette of thePD system of FIG. 1.

FIG. 7 is a side view of the PD cassette of the PD system of FIG. 1,showing adhesive disposed on the portion of the membrane overlying apump chamber of the cassette.

FIG. 8 is a perspective view from the membrane side of the PD cassetteof the PD system of FIG. 1 with eyeglass-shaped release paper coveringand adhered to the adhesive regions on the membrane.

FIG. 9 is a plan view from the membrane side of the PD cassette of thePD system of FIG. 1 with eyeglass-shaped release paper covering andadhered to the adhesive regions on the membrane.

FIG. 10 is a plan view of the PD cassette of FIGS. 8 and 9 showing theeyeglass-shaped release paper being removed from the adhesive regions onthe membrane.

FIG. 11 is a partial perspective view of the PD cassette in the cassettecompartment of the PD cycler of the PD system of FIG. 1.

FIGS. 12A-12C are diagrammatic cross-sectional views of the PD cassettein the cassette compartment of the PD cycler of the PD system of FIG. 1,during different phases of operation.

FIGS. 13A-13C illustrate various fluid flow paths through the PDcassette of the PD system of FIG. 1 during a PD treatment.

FIGS. 14A-14C illustrate a method of making eyeglass-shaped compositesof adhesive regions disposed between and adhered to two release papers.

FIG. 15 is a perspective view of an eyeglass-shaped composite made usingthe method illustrated in FIGS. 14A-14C, showing one of the releasepapers of the composite being removed from the adhesive regions.

FIG. 16 is a perspective view of the eyeglass-shaped composite of FIG.15 (with one of the release papers removed) being applied to themembrane of the PD cassette of the PD system of FIG. 1.

FIG. 17 is a plan view of a PD cassette with discrete release papersincluding pull tabs covering and adhered to the adhesive regions.

FIG. 18 is a plan view of a PD cassette with a release paper coveringand adhered to the adhesive regions. The release paper is sized to coversubstantially the entire surface of the cassette and includes printedtext on its surface.

FIG. 19 is a side view of a piston head of the PD system of FIG. 1 and aPD cassette with a three-layer adhesive composite adhered to a membraneof the cassette.

DETAILED DESCRIPTION

Referring to FIG. 1, a peritoneal dialysis (“PD”) system 100 includes aPD cycler (also referred to as a PD machine) 102 seated on a cart 104.Referring also to FIG. 2, the PD cycler 102 includes a housing 106, adoor 108, and a cassette interface 110 that mates with a disposable PDcassette 112 when the cassette 112 is disposed within a cassetteenclosure 114 formed between the cassette interface 110 and the closeddoor 108. A heater tray 116 is positioned on top of the housing 106. Theheater tray 116 is sized and shaped to accommodate a bag of PD solution(e.g., a 5 liter bag of PD solution). The PD cycler 102 also includes atouch screen 118 and additional control buttons 26 that can be operatedby a user (e.g., a patient) to allow, for example, set-up, initiation,and/or termination of a PD treatment.

PD solution bags 122 are suspended from fingers on the sides of the cart104, and a heater bag 124 is positioned in the heater tray 116. The PDsolution bags 122 and the heater bag 124 are connected to the cassette112 via PD solution bag lines 126 and a heater bag line 128,respectively. The PD solution bag lines 126 can be used to pass PDsolution from PD solution bags 122 to the cassette 112 during use, andthe heater bag line 128 can be used to pass PD solution back and forthbetween the cassette 112 and the heater bag 124 during use. In addition,a patient line 130 and a drain line 132 are connected to the cassette.The patient line 130 can be connected to a patient's abdomen via acatheter and can be used to pass PD solution back and forth between thecassette 112 and the patient during use. The drain line 132 can beconnected to a drain or drain receptacle and can be used to pass PDsolution from the cassette 112 to the drain or drain receptacle duringuse.

FIG. 3 shows a more detailed view of the cassette interface 110 and thedoor 108 of the PD cycler 102. As shown, the PD cycler 102 includespistons with substantially hemispherical piston heads 134A, 134B thatcan be axially moved within piston access ports 136A, 136B formed in thecassette interface 110. The piston heads 134A, 134B are made ofpolyoxymethylene (marketed under the tradename Delrin available fromDupont of Wilmington, Del.). The hemispherical shape of the piston heads134A, 134B can be achieved using machining techniques. Alternatively oradditionally, the hemispherical shape of the piston heads 134A, 134B canbe formed using molding or casting techniques. The pistons includepiston shafts that are coupled to motors that can be operated to movethe piston heads 134A, 134B axially inward and outward within the pistonaccess ports 136A, 136B. As discussed below, when the cassette 112(shown in FIGS. 2 and 4-7) is positioned within the cassette enclosure114 with the door 108 closed, the piston heads 134A, 134B of the PDcycler 102 align with pump chambers 138A, 138B of the cassette 112. Thepiston heads 134A, 134B, as described in greater detail below, can beadhered to portions of a membrane 140 overlying the pump chambers 138A,138B of the cassette 112. As a result, the piston heads 134A, 134B canbe moved in the direction of the cassette 112 to force the membrane 140into the volume defined by the pump chambers 138A, 138B, causing thevolume defined by the pump chambers to decrease and forcing fluid out ofthe pump chambers 138A, 138B. The piston heads 134A, 134B can also beretracted away from the cassette 112 and out of the volume defined bythe pump chambers 138A, 138B such that the volume defined by the pumpchambers 138A, 138B increases and fluid is drawn into the pump chambers138A, 138B.

The PD cycler 102 also includes multiple inflatable members 142positioned within inflatable member access ports 144 in the cassetteinterface 110. The inflatable members 142 align with depressible domeregions 146 of the cassette 112 when the cassette 112 is positionedwithin the cassette enclosure 114. While only one of the inflatablemembers 142 is labeled in FIG. 3, it should be understood that the PDcycler 102 includes an inflatable member associated with each of thedepressible dome regions 146 of the cassette 112 (shown in FIG. 5). Theinflatable members 142 act as valves to direct fluid through thecassette 112 in a desired manner during use. In particular, theinflatable members 142 bulge outward beyond the surface of cassetteinterface 110 and into contact with the depressible dome regions 146 ofthe cassette 112 when inflated, and retract into the inflatable memberaccess ports 144 and out of contact with the cassette 112 when deflated.By inflating certain inflatable members 142 to depress their associateddome regions 146 on the cassette 112, certain fluid flow paths withinthe cassette 112 can be blocked off. Thus, fluid can be pumped throughthe cassette 112 by actuating the piston heads 134A, 134B, and can beguided along desired flow paths within the cassette 112 by selectivelyinflating and deflating the inflatable members 142.

Still referring to FIG. 3, locating pins 148 extend from the cassetteinterface 110. When the door 108 is in the open position, the cassette112 can be loaded onto the cassette interface 110 by positioning the topportion of the cassette 112 under the locating pins 148 and pushing thebottom portion of the cassette 112 toward the cassette interface 110.The cassette 112 is dimensioned to remain securely positioned betweenthe locating pins 148 and a lower ledge 150 extending from the cassetteinterface 110 to allow the door 108 to be closed over the cassette 112.The locating pins 148 help to ensure that the pump chambers 138A, 138Bof the cassette 112 are aligned with the piston heads 134A, 134B whenthe cassette 112 is positioned in the cassette enclosure 114 between theclosed door 108 and the cassette interface 110.

The door 108 defines recesses 152A, 152B that substantially align withthe piston heads 134A, 134B when the door 108 is in the closed position.When the cassette 112 is positioned within the cassette enclosure 114,hemispherical projections 154A, 154B of the cassette 112 (shown in FIG.4), which partially define the pump chambers 138A, 138B, fit within therecesses 152A, 152B. In this configuration, the portions of the door 108forming the recesses 152A, 152B can support the hemisphericalprojections 154A, 154B while the planar surface of the door 108 cancounteract the force of the inflatable members 142 and thus allow theinflatable members 142 to actuate the depressible dome regions 146 onthe cassette 112.

The PD cycler 102 includes various other features not described here.Further details regarding the PD cycler 102 and its various componentscan be found in U.S. Patent Application Publication No. 2007/0112297,which is incorporated by reference herein.

Referring to FIGS. 4-7, the cassette 112 includes a tray-like rigid base156 and the flexible membrane 140, which is attached to (e.g., thermallybonded to, adhered to) the periphery of the base 156. The base is madeof polypropylene, and can be formed using machining, molding, and/orcasting techniques. As shown in FIGS. 4 and 7, the hemispherical, hollowprojections 154A, 154B of the base 156 are substantially symmetricallypositioned with respect to the center vertical axis of the cassette 112.The hemispherical projections 154A, 154B extend away from the membrane140 and are sized and shaped to fit within the recesses 152A, 152B inthe door 108 of the PD cycler 102. The membrane 140 cooperates with thebase 156 to form the pump chambers 138A, 138B. In particular, the volumebetween the membrane 140 and the projections 154A, 154B define the pumpchambers 138A, 138B. The base 156 further includes raised structuralfeatures that extend toward and into contact with the inner surface ofthe membrane 140. The membrane 140 cooperates with the raised structuralfeatures extending from the base 156 to form a series of fluid pathways158 and the multiple, depressible dome regions 146, which are widened(e.g., substantially circular) portions of the fluid pathways. At eachdepressible dome region 146, the membrane 140 can be deflected tocontact the base 156. Such contact can substantially impede (e.g.,prevent) the flow of PD solution along the pathway 158 associated withthat dome region 146 during use. Thus, as described in further detailbelow, the flow of PD solution through the cassette 112 can becontrolled through the selective depression of the depressible domeregions 146 by selectively inflating the inflatable members 142 of thePD cycler 102.

The rigidity of the base 156 helps to hold the cassette 112 in placewithin the cassette enclosure 114 of the PD cycler 102 and to preventthe hemispherical projections 154A, 154B and the other raised featuresof the cassette 112 from flexing and deforming in response to changes inpressure within the cassette 112 during use. The rigidity of the base156 also allows the hemispherical projections 154A, 154B to resistdeformation by the piston heads 134A, 134B during use.

The fluid pathways 158 in the cassette 112 lead from the pumpingchambers 138A, 138B to connectors 160 positioned along the bottom edgeof the cassette 112. The connectors 160 are positioned asymmetricallyalong the width of the cassette 112. The asymmetrical positioning of theconnectors 160 helps to ensure that the cassette 112 will be properlypositioned in the cassette enclosure 114 with the membrane 140 and ofthe cassette 112 facing the cassette interface 110. The connectors 160are configured to receive fittings on the ends of the PD solution baglines 126, the heater bag line 128, the patient line 130, and the drainline 132. These fittings are double male fittings. One end of thefitting can be inserted into and bonded to its respective line and theother end can be inserted into and bonded to its associated connector160. By permitting the PD solution bag lines 126, the heater bag line128, the patient line 130, and the drain line 132 to be connected to thecassette, as shown in FIGS. 1 and 2, the connectors 160 allow PDsolution to flow into and out of the cassette 112 during use.

Still referring to FIGS. 4-7, the membrane 140 of the cassette 112includes three layers. The inner and outer layers of the laminate areformed of a compound that is made up of 60 percent Septon® 8004thermoplastic rubber (i.e., hydrogenated styrenic block copolymer) and40 percent ethylene. The middle layer is formed of a compound that ismade up of 25 percent Tuftec® H1062 (SEBS: hydrogenated styrenicthermoplastic elastomer), 40 percent Engage® 8003 polyolefin elastomer(ethylene octene copolymer), and 35 percent Septon® 8004 thermoplasticrubber (i.e., hydrogenated styrenic block copolymer). The thickness ofthe membrane 140 is selected so that the membrane 140 has sufficientflexibility to flex toward the base 156 in response to the force appliedto the membrane 140 by the piston heads 134A, 134B. For example, themembrane 140 can be about 0.100 inch to about 0.150 inch in thickness.

Adhesive 161 is disposed on regions 162A, 162B of the membrane 140 thatoverlie the pump chambers 138A, 138B. The adhesive 161 is a doublecoated synthetic rubber adhesive tape manufactured by 3M as part number9443NP. The properties of the adhesive 161 allow the adhesive 161 toachieve a temporary adhesive attachment with the piston heads 134A, 134Bwhen the piston heads 134A, 134B are brought into contact with theadhesive regions during use. The attachment between the adhesive 161 andthe piston heads 134A, 134B is sufficiently strong to allow the adhesiveto remain attached to the piston heads 134A, 134B as the piston heads134A, 134B are reciprocated during use. At the same time, the attachmentbetween the adhesive 161 and the piston heads 134A, 134B can be readilybroken by retracting the piston heads 134A, 134B by a greater distancethan they are retracted during treatment and with a force that exceedsthe adhesion force between the adhesive 161 and the piston heads 134A,134B.

The adhesion strength of the adhesive 161 to polyester is about 89Oz./in. (about 97 N/100 mm), as tested using the ASTM D3330 test (90degree, 2 mil Al foil, 72 hour room temperature (RT)). The adhesionstrength of the adhesive 161 to polypropylene is about 85 Oz./in. (about93 N/100 mm), as tested using the ASTM D3330 test (90 degree, 2 mil Alfoil, 72 hour RT). The adhesion strength of the adhesive 161 topolycarbonate is about 101 Oz./in. (about 110 N/100 mm), as tested usingthe ASTM D3330 test (90 degree, 2 mil Al foil, 72 hour RT). The adhesionstrength of the adhesive 161 to stainless steel is about 93 Oz./in.(about 101 N/100 mm), as tested using the ASTM D3330 test (90 degree, 2mil Al foil, 15 minute RT). The adhesion strength of the adhesive 161 tostainless steel is about 97 Oz./in. (about 106 N/100 mm), as testedusing the ASTM D3330 test (90 degree, 2 mil Al foil, 72 hour RT). Theadhesion strength of the adhesive 161 to stainless steel is about 126Oz./in. (about 137 N/100 mm), as tested using the ASTM D3330 test (90degree, 2 mil Al foil, 72 hour 158° F. (70° C.)). The adhesion strengthof the adhesive 161 to stainless steel is about 206 Oz./in. (about 224N/100 mm), as tested using the ASTM D3330 test (180 degree, 2 mil Alfoil, 72 hour RT).

During use, the cassette 112 is secured within the cassette enclosure114 by positioning the adhesive-carrying side of the cassette 112adjacent to the cassette interface 110 of the PD cycler 102 and closingthe door 108 over the cassette 112. As noted above, the piston heads134A, 134B align with the pump chambers 138A, 138B of the cassette 112when the cassette 112 is positioned in the cassette enclosure 114between the cassette interface 110 and the closed door 108. Thus, withthe cassette 112 secured in the cassette enclosure 114, the piston heads134A, 134B can extend into the enclosure 114 to contact the adhesive 161disposed on regions 162A, 162B of the flexible membrane 140 and becometemporarily adhesively attached to the membrane 140 of the cassette 112.The adhesive 161, the material of the piston heads 134A, 134B, and thematerial of the membrane 140 are selected so that the adhesive 161 has agreater adhesion or affinity to the membrane 140 than to the pistonheads 134A, 134B. The adhesive attachment between the piston heads 134A,134B and the membrane 140 causes the regions 162A, 162B of the membrane140 overlying the pump chambers 138A, 138B to move along with the pistonheads 134A, 134B, and thus allows PD solution to be drawn into or forcedout of the pump chambers of the cassette 112 in response to piston headmovement during treatment. Movement of those regions 162A, 162B of themembrane 140 overlying the pump chambers 138A, 138B (e.g., throughmovement of piston heads 134A, 134B) changes the internal volume of thepump chambers 138A, 138B. For example, movement of the membrane 140toward the rigid base 156 decreases the fluid volume stored in each ofthe pump chambers 138A, 138B, and thus forces some of the PD solutionout of the cassette 112 during treatment. Similarly, movement of themembrane 140 away from the base 156 increases the fluid volume stored inthe pump chambers 138A, 138B, and thus draws PD solution into thecassette 112 during treatment.

By retracting the piston heads 134A, 134B farther than they areretracted during treatment (i.e., farther than they are retracted todraw fluid into the pump chambers 138A, 138B during treatment) and witha force that exceeds the adhesion force between the piston heads 134A,134B and the adhesive 161, the piston heads 134A, 134B can be detachedfrom the adhesive 161 and the membrane 140. The piston heads 134A, 134Bcan, for example, be fully retracted into the piston access ports 136A,136B to detach the piston heads 134A, 134B from the adhesive 161 and themembrane 140. In some cases, the piston heads 134A, 134B are retractedat least about 1.0 centimeters (e.g., at least about 1.5 centimeters,about 1.0 centimeters to about 2.5 centimeters, about 1.5 centimeters)away from the plane in which the membrane 140 lies in its undeformedstate with the cassette 112 positioned in the cassette enclosure 114.Retracting the piston heads 134A, 134B to this position can help toensure that the piston heads 134A, 134B detach from the adhesive 161.

The movement of the piston heads 134A, 134B away from the cassette 112exerts a tensile stress on the adhesive 161. The piston heads 134A, 134Bremain substantially adhered to the adhesive 161 if the tensile forcesexerted by the piston heads 134A, 134B are less than the adhesionstrength of the adhesive 161 to the piston heads 134A, 134B and/or thepiston heads 134A, 134B are retracted by a distance less than thedistance required to detach the piston heads 134A, 134B from theadhesive 161. The piston heads 134A, 134B detach from the adhesive 161if the tensile forces exerted by the piston heads 134A, 134B are greaterthan the adhesion strength of the adhesive 161 to the piston heads 134A,134B and the piston heads 134A, 134B are retracted by a sufficientdistance to detach the piston heads 134A, 134B from the adhesive 161.

To permit the piston heads 134A, 134B to be detached from the adhesive161 while the adhesive 161 remains attached to the membrane 140 of thecassette 112, the adhesive 161, the piston heads 134A, 134B, and themembrane 140 are formed of materials such that the adhesion strength oraffinity of the membrane 140 to the adhesive 161 is greater than theadhesion strength or affinity of the piston heads 134A, 134B to theadhesive 161. To reduce the likelihood that the adhesive 161 will detachfrom the membrane 140 (and remain attached to the piston heads 134A,134B) while attempting to detach the piston heads 134A, 134B from theadhesive (i.e., by retracting the piston heads 134A, 134B), the adhesive161, the piston heads 134A, 134B, and the membrane 140 are formed ofmaterials such that the adhesion strength or affinity of the adhesive161 to the membrane 140 is substantially greater (e.g., at least abouttwo times greater (e.g., about two to about three times greater)) thanthe adhesion strength or affinity of the adhesive 161 to the pistonheads 32A, 23B.

As a result of the selected materials of the adhesive 161, the pistonheads 134A, 134B, and the membrane 140, the piston heads 134A, 134B canbe detached from the adhesive 161 in a manner similar to that in which a3M Post-It® note is detached from a surface (e.g., desktop or sheet ofpaper). The material selection can, for example, ensure that aninsignificant amount of adhesive (e.g., no adhesive) remains attached tothe piston heads 134A, 134B after the piston heads 134A, 134B aredetached from the adhesive 161 and the membrane 140.

In some implementations, the adhesive 161 is capable of maintainingcontact with the piston heads 134A, 134B for up to 24 hours at a pumpspeed of about 200 ml/min to about 600 ml/min.

In certain implementations, the adhesive 161 is disposed substantiallyuniformly over regions 162A, 162B. Such a substantially uniformdistribution of the adhesive 161 can reduce the likelihood that themembrane 140 will separate or decouple from the piston heads 134A, 134Bduring normal operation. Additionally or alternatively, such asubstantially uniform distribution of adhesive can improve the accuracyin calculating the volume of pump chambers 138A, 138B based on theposition of the piston heads 134A, 134B, which can be used to closelytrack the volume of PD solution pumped out of and drawn into the pumpchambers 138A, 138B during treatment.

In addition to securing the piston heads 134A, 134B to the membrane 140of the cassette 112, the adhesive 161 can reduce the likelihood of fluidintrusion into the PD cycler 102 during use. For example, because theadhesive 161, rather than vacuum pressure, is used to retract theportions of the membrane 140 overlying the pump chambers 138A, 138B inorder to draw fluid into the pump chambers 138A, 138B, the possibilityof fluid being drawn through the membrane 140 as a result of excessivevacuum pressure is eliminated. In addition, in some cases, the adhesive161 acts as a substantially impermeable layer that restricts (e.g.,prevents) PD solution from passing through the cassette 112 into the PDcycler 102 in regions 162A, 162B. For example, to the extent that themembrane 140 is semi-permeable or becomes semi-permeable (e.g., throughrepeated flexing during use), the adhesive 161 can form a substantiallyliquid tight seal with the membrane 140 across regions 162A, 162B of themembrane 140.

As shown in FIGS. 8 and 9, when initially provided to the user, thecassette 112 includes a generally eyeglass-shaped release paper 164(e.g., wax-coated paper) that covers the adhesive 161 overlying the pumpchambers 138A, 138B. Such a release paper can, for example, preventdebris and contaminants from collecting on the adhesive 161 duringstorage and handling of the cassette 112. The release paper 164 can bepeeled off of the cassette 112 to expose the adhesive 161 prior toloading the cassette 112 into the cassette enclosure 114 of the PDcycler 102.

The release paper 164 includes two circular portions 166A, 166B and aconnector portion 168 that extends between the two circular portions166A, 166B. The circular portions 166A, 166B cover the adhesive ladenregions 162A, 162B of the cassette membrane 140. The release paper 164also includes a pull tab 170 that extends beyond the outer boundary ofthe adhesive 161 such that the pull tab 170 is not attached to theadhesive 161. A user can remove the release paper 164 to expose theadhesive 161 by pulling the pull tab 170. As the pull tab 170 is pulledaway from the cassette 112, the connector portion 168 of the releasepaper 164 facilitates removal of both circular portions 166A, 166B ofthe release paper 164 through a single, continuous motion.

Referring to FIG. 10, to prepare the PD cassette 112 for use, therelease paper 164 is first peeled away from the membrane 140 of thecassette 112 by grasping and pulling the pull tab 170. This exposes theadhesive 161 initially positioned beneath the release paper 164. Therelease paper 164 can be discarded after removing it from the cassette112.

As shown in FIG. 11, the door 108 of the PD cycler 102 is then opened toexpose the cassette interface 110, and the cassette 112 is positionedadjacent to the interface 110 such that the adhesive 161 on the regions162A, 162B of the membrane 140 overlying the pump chambers 138A, 138B ofthe cassette 112 is facing and is aligned with the piston heads 134A,134B. In order to ensure that the adhesive 161 aligns with the pistonheads 134A, 134B, the cassette 112 is positioned between the locatingpins 148 and the lower ledge 150 extending from the cassette interface110. The asymmetrical positioning of the connectors 160 of the cassetteact as a keying feature that reduces the likelihood that the cassette112 will be installed with the adhesive facing in the wrong direction(e.g., facing outward toward the door 108). Additionally oralternatively, the locating pins 148 can be dimensioned to be less thanthe maximum protrusion of the hemispherical projections 154A, 154B suchthat the cassette 112 cannot contact the locating pins 148 if theadhesive covered regions 162A, 162B of the membrane 140 are facingoutward toward the door 108.

While loading the cassette 112 into the PD cycler 102, the piston heads134A, 134B are completely retracted within the piston access ports 136A,136B. This positioning of the piston heads 134A, 134B can reduce thelikelihood of damage to the piston heads 134A, 134B during installationof the cassette 112. This positioning of the piston heads 134A, 134B canalso facilitate positioning the cassette 112 against the cassetteinterface 110 before closing the door 108. For example, this positioningcan help to ensure that the adhesive 161 is not inadvertently attachedto the piston heads 134A, 134B prior to properly positioning thecassette 112 within the cassette enclosure 114.

Referring to FIG. 12A, with the cassette 112 positioned adjacent to thecassette interface 110, the door 108 is closed over the cassette 112such that the cassette 112 is substantially contained within thecassette enclosure 114 between the door 108 and the cassette interface110. As shown, the hemispherical projections 154A, 154B of the cassette112 fit within the recesses 152A, 152B in the door 108. Because the PDsystem 100 does not require a vacuum system to move the portions 162A,162B of the membrane 140 overlying the pump chambers 138A, 138B, asubstantially airtight seal between the door 108 and the cassetteinterface 110 is typically not required. Thus, as compared to systemsincluding a vacuum system adapted to retract portions of the cassettemembrane overlying pump chambers, the door sealing mechanism of the PDcycler 102 can be simpler and more cost effective.

As shown in FIG. 12B, with the cassette 112 secured within the enclosure114, the piston heads 134A, 134B are moved outward (e.g., to asubstantially fully extended position) to contact the adhesive 161disposed on the regions 162B, 162B of the cassette membrane 140. In thisfully extended position, the inner surface of the membrane 140 comesinto contact or near contact with the inner surface of the hemisphericalprojections 154A, 154B of the rigid base 156 of the cassette 112. Thecontact between the piston heads 134A, 134B and the adhesive 161 causesthe adhesive 161 to adhere to the piston heads 134A, 134B. Because theadhesive 161 is also adhered to the membrane 140 of the cassette 112,the adhesive 161 secures the piston heads 134A, 134B to the membrane140.

With the piston heads 134A, 134B adhesively attached to the membrane140, PD solution can be drawn into the pump chambers 138A, 138B of thecassette 112 by retracting the membrane 140 along with the piston heads134A, 134B to increase the volume of the pump chambers 138A, 138B, asshown in FIG. 12C. The fluid can then be forced out of the pump chambers138A, 138B by again returning the piston heads 134A, 134B to theposition shown in FIG. 12B, causing the membrane 140 to move toward therigid base 156 and thus decreasing the volume of the pump chambers 138A,138B. As noted above, while forcing PD solution into and out of the pumpchambers 138A, 138B, certain inflatable members 142 of the PD cycler 102can be selectively inflated to direct the pumped PD solution alongdesired pathways in the cassette 112.

Referring back to FIGS. 1 and 2, during PD treatment, the patient line130 is connected to a patient's abdomen via a catheter, and the drainline 132 is connected to a drain or drain receptacle. The PD treatmenttypically begins by emptying the patient of spent PD solution thatremains in the patient's abdomen from the previous treatment. To dothis, the pump of the PD cycler 102 is activated to cause the pistonheads 134A, 134B to reciprocate and selected inflatable members 142 areinflated to cause the spent PD solution to be drawn into the pumpchambers 138A, 138B of the cassette 112 from the patient and then pumpedfrom the pump chambers 138A, 138B to the drain via the drain line 132.This flow path of the spent PD solution through the fluid pathways 158in the cassette 112 is shown in FIG. 13A.

After draining the spent PD solution from the patient, heated PDsolution is transferred from the heater bag 124 to the patient. To dothis, the pump of the PD cycler 102 is activated to cause the pistonheads 134A, 134B to reciprocate and certain inflatable members 142 ofthe PD cycler 102 are inflated to cause the spent PD solution to bedrawn into the pump chambers 138A, 138B of the cassette 112 from theheater bag 124 via the heater bag line 128 and then pumped from the pumpchambers 138A, 138B to the patient via the patient line 130. This flowpath of the PD solution through the fluid pathways 158 in the cassette112 is shown in FIG. 13B.

Once the PD solution has been pumped from the heater bag 124 to thepatient, the PD solution is allowed to dwell within the patient for aperiod of time. During this dwell period, toxins cross the peritoneuminto the PD solution from the patient's blood. As the PD solution dwellswithin the patient, the PD cycler 102 prepares fresh dialysate fordelivery to the patient in a subsequent cycle. In particular, the PDcycler 102 pumps fresh PD solution from one of the four full PD solutionbags 122 into the heater bag 124 for heating. To do this, the pump ofthe PD cycler 102 is activated to cause the piston heads 134A, 134B toreciprocate and certain inflatable members 142 of the PD cycler 102 areinflated to cause the PD solution to be drawn into the pump chambers138A, 138B of the cassette 112 from the selected PD solution bag 122 viaits associated line 126 and then pumped from the pump chambers 138A,138B to the heater bag 124 via the heater bag line 128. This flow pathof the PD solution through the fluid pathways 158 in the cassette 112 isshown in FIG. 13C.

After the PD solution has dwelled within the patient for the desiredperiod of time, the spent PD solution is pumped from the patient to thedrain. The heated PD solution is then pumped from the heater bag 124 tothe patient where it dwells for a desired period of time. These stepsare repeated with the PD solution from two of the three remaining PDsolution bags 122. The PD solution from the last PD solution bag 122 istypically delivered to the patient and left in the patient until thesubsequent PD treatment.

The PD cycler is typically used in an alternating pumping mode in whichone piston head is protracted while the other piston head is retracted.Thus, as fluid drawn into one pumping chamber, fluid is simultaneouslyexpelled from the other pumping chamber.

The adhesive attachment between the piston heads 134A, 134B and themembrane 140 can result in a substantially direct correlation betweenthe position of the piston heads 134A, 134B and the volume of fluiddrawn into and pumped out of the pump chambers 138A, 138B of thecassette 112. Such a direct correlation can improve the speed andaccuracy of volumetric calculations of PD solution drawn into and pumpedout of the cassette 112.

After completion of the PD treatment, the piston heads 134A, 134B areretracted away from the cassette 112 (e.g., perpendicular to thecassette 112) to a distance sufficient to allow the adhesive 161 todetach from the piston heads 134A, 134B and with a force that exceedsthe adhesion strength or affinity of the adhesive 161 to the pistonheads 134A, 134B. With this motion, the piston heads 134A, 134B becomecompletely detached from the adhesive 161. Because the adhesion strengthor affinity of the adhesive 161 to the membrane 140 is greater than theadhesion strength or affinity of the adhesive 161 to the piston heads134A, 134B, the adhesive 161 remains adhered to the cassette 112 afterthe piston heads 134A, 134B have been detached. This helps to reduce oreliminate adhesive build-up on the piston heads 134A, 134B throughrepeated use. With the piston heads 134A, 134B detached from theadhesive 161, the door 108 of the PD cycler 102 is opened to expose thecassette 112, and the cassette 112, including the adhesive thereon, isremoved from the cassette enclosure 114 by moving the bottom portion ofthe cassette 112 away from the cassette interface 110 and disengagingthe top portion of the cassette 112 from the locating pins 148. In somecases, the cassette 112 is then discarded along with the fluid linesattached to the cassette 112. Because the adhesive 161 detaches from thepiston heads 134A, 134B, it will generally be unnecessary for the userto clean the piston heads 134A, 134B prior to a subsequent use with anew cassette.

FIGS. 14A-14C illustrate a method of preparing eyeglass-shapedcomposites of adhesive and release paper that are used to apply theadhesive 161 and release paper 164 to the membrane 140 of the cassette112. Referring to FIG. 14A, the adhesive 161 is first sprayed onto thetop surface of a sheet of release paper (e.g., a sheet of wax-coatedpaper) 200 by a sprayer 202 including two spray nozzles 204. Theadhesive 161 is sprayed onto the sheet of release paper 200 in pairs ofcircular adhesive regions 206 that are longitudinally spaced from eachother along the sheet of release paper 200. The sprayer 202 isintermittently activated while the sheet of release paper 200 iscontinuously passed under the nozzles 204 to create the longitudinallyspaced adhesive regions 206. The circular adhesive regions 206 withineach pair are sized to correspond to the size of the pump chambers 138A,138B of the cassette 112 (i.e., the largest diameter of the pumpchambers 138A, 138B), and the circular adhesive regions 206 within eachpair are laterally spaced from one another across the sheet of releasepaper 200 by substantially the same distance that the pump chambers138A, 138B of the cassette 112 are laterally spaced from one another. Asan alternative to using two separate nozzles configured to create thecircular adhesive regions, a large surface area sprayer can be equippedwith a stencil with circular shaped openings such that only adhesivepassing though the openings will reach the sheet of release paper 200while the remaining adhesive accumulates on the stencil. In addition, asan alternative to spraying the adhesive onto the sheet of release paper200, any of various other techniques for applying the adhesive to thesheet of release paper 200 can be used. Examples of other techniquesinclude dip coating, pouring, painting, etc.

As shown in FIG. 14B, after applying the adhesive circular regions tothe top surface of the sheet of release paper 200, another sheet ofrelease paper 208 is disposed over the circular adhesive regions 206 andsecured to the first sheet of release paper 200 by the adhesive regions206. The resulting composite sheet includes a discontinuous layer ofcircular adhesive regions 206 sandwiched between the two sheets ofrelease paper 200, 208.

Referring to FIG. 14C, a generally eyeglass-shaped cutter 210 is thenforced through the composite sheet at multiple, longitudinally spacedpositions along the sheet to form multiple generally eyeglass-shapedcomposites. The cutter 210 includes a sharp cutting edge that extendsaround its periphery on its lower surface. The cutter 210 is manipulatedto cut through the composite along a path that encompasses each of thepairs of adhesive regions 206. To do this, the composite sheet is passedunder the cutter 210 until one of the pairs of adhesive regions 206within the composite sheet lies directly beneath the cutter 210 withcutting edges of the cutter 210 surrounding the pair of adhesive regions206. At this point, the movement of the composite sheet is paused, andthe cutter 210 punches through the composite sheet to form aneyeglass-shaped composite. This process is repeated to produce multipleeyeglass-shaped composites. Each eyeglass-shaped composite includes twocircular adhesive shaped regions 206 sandwiched between twoeyeglass-shaped layers of release paper. Each of the two layers ofrelease paper includes a pull tab 212 that extends beyond the adhesiveregions 206 to facilitate removal of the release paper by a user.

FIG. 15 shows one of the eyeglass-shaped composites produced from theabove described method. As shown in FIG. 15, to permit the adhesiveregions 206 to be secured to the regions 162A, 162B of the membrane 140overlying the pump chambers 138A, 138B of the cassette 112, one of therelease papers is peeled away from the adhesive by pulling on its pulltab 212.

Referring to FIG. 16, the exposed adhesive regions are then applied tothe portions 162A, 162B of the membrane 140 overlying the pump chambers138A, 138B of the cassette 112. A set of fluid lines is then attached tothe cassette, and the assembly of the cassette 112 and the attachedfluid lines is packaged in a container (e.g., a bag and a box) fordelivery to a user. At this point, the cassette 112, including theadhesive regions and release paper thereon, the fluid lines, and thepackaging is sterilized with ethylene oxide (ETO). The release paperadvantageously limits contact between the adhesive regions and the ETOduring this sterilization process, which helps to maintain the integrityof the adhesive. Alternatively or additionally, the cassette 112 can besterilized using other sterilization techniques, such as gamma or e-beamsterilization.

While certain implementations have been described, other implementationsare possible.

While the release paper 164 has been described as having a generallyeyeglass shape, other types of release papers can be used. In someimplementations, as shown in FIG. 17, for example, two substantiallycircular shaped release papers 364 are used to cover the adhesiveregions. Each of the release papers 364 includes a pull tab 370 thatextend beyond the outer boundary of the adhesive region to facilitateremoval of the release paper 364 from the adhesive.

While the release papers described above are shaped to coversubstantially only those regions of the cassette membrane 140 thatinclude adhesive thereon, the release paper can be dimensioned to coverany of various different areas of the cassette membrane 140. In someimplementations, as shown in FIG. 18, for example, a release paper 464covers substantially the entire membrane 140 of the cassette 112. Thiscan help protect the cassette membrane 140 from damage and/orcontamination prior to use. One of the corners of the release paper 464can be used as a pull tab to facilitate removal of the release paper 464from the adhesive. As shown, the release paper 464 bears printed textthat reminds the user to remove the release paper 464 before use. Any ofthe various other release papers described herein could include similartext.

While the adhesive 161 has been described as being initially disposed onthe membrane 140 of the cassette 112, other arrangements are possible.In some implementations, for example, the adhesive 161 is initiallydisposed on the piston heads 134A, 134B. In certain implementations, theadhesive 161 remains on the piston heads 134A, 134B after the cassette112 has been removed from the cassette enclosure 114 of the PD cycler102. For example, the adhesive 161, the membrane 140 of the cassette112, and the piston heads 134A, 134B can be formed of materials suchthat the adhesive 161 has a greater adhesion or affinity with the pistonheads 134A, 134B than with the membrane 140. Because the adhesive 161remains on the piston heads 134A, 134B, the adhesive 161 can be reusedthrough multiple PD treatments, or the user can remove the adhesive 161from the piston heads 134A, 134B between treatments. In otherimplementations, the materials of the adhesive 161, the membrane 140 ofthe cassette 112, and the piston heads 134A, 134B can be selected suchthat the adhesive 161 has a greater adhesion or affinity with themembrane 140 than with the piston heads 134A, 134B. In such cases, theadhesive 161 would ultimately remain adhered to the cassette 112 that isremoved from the PD cycler 102 and discarded.

While the adhesive differential between the piston heads 134A, 134B andthe membrane 140 has been described as being achieved through acombination of materials including forming the piston heads 134A, 134Bof polyoxymethylene and the membrane 140 from the above-describedmulti-layer laminate while using a synthetic rubber adhesive, othermaterial combinations that provide levels of adhesion between theadhesive and the piston heads and between the adhesive and the cassettemembrane to allow the piston heads to retract the membrane duringtreatment and to allow the piston heads to be detached from the membraneafter treatment without detaching the adhesive from the cassettemembrane can be used.

In certain implementations, for example, the adhesive can be formed ofany of various other types of materials that have adhesion propertiessimilar to the synthetic rubber adhesive described above. For example,the adhesive can be a natural rubber adhesive or an acrylic adhesive.The piston heads 134A, 134B can be formed of one or more polyvinylchlorides (PVC), polyamides, polycarbonates, ethyl vinyl acetates,and/or polysulfones. The membrane 140 can be formed of any of varioustypes of polyolefins (e.g., high density polyethylenes (HDPE), lowdensity polyethylenes (LDPE), or combinations of HDPE and LDPE) and/orpolyvinylchlorides (PVC).

In certain implementations, the adhesive 161 is formed of natural rubberadhesive, the piston heads 134A, 134B are formed of polyoxymethyleneplastic, and the membrane 140 is formed of polyolefin. In otherimplementations, the adhesive 161 is formed of acrylic co polymer, thepiston heads 134A, 134B are formed of polycarbonate, and the membrane140 is formed of PVC.

While the membrane 140 of the cassette 112 has been described asincluding three layers, the membrane of the cassette can alternativelyinclude fewer than three layers. For example, the membrane can includetwo layers or only a single layer. Alternatively, the membrane of thecassette can include more than three layers.

While the base 156 of the cassette 112 has been described as beingformed of polypropylene, the base 156 can be formed of any of variousdifferent rigid materials that are capable of being securely attached(e.g., thermally bonded, adhesively bonded) to the cassette membrane140. In some implementations, for example, the base 156 is formed ofpolyvinyl chloride, polycarbonate, polysulfone, or other medical gradeplastic materials.

While the piston heads 134A, 134B have been described as being formed ofa single material that has a desired affinity for the adhesive, othertypes of piston head constructions can be used. For example, in someimplementations, the piston head includes a core on which an outer layeror coating is applied. In such implementations, the outer layer orcoating can be formed of a material that has the desired affinity forthe adhesive while the core of the piston head can be formed of adifferent material that does not have the desired affinity for theadhesive. The outer layer or coating can, for example, be formed of anyof the materials described above with regard to piston heads 134, 134B,and the core can be formed of any of various other materials, includingpolymers, metals, and/or alloys.

While the adhesion or affinity differential between the piston heads134A, 134B and the membrane 140 has been described as being achievedthrough material selection, other methods of achieving the adhesiondifferential can alternatively or additionally be used. For example, thepiston heads 134A, 134B can be roughened (e.g., through etching, throughroughness built into a mold) to increase the surface area of the pistonheads 134A, 134B. As compared to piston heads having smooth surfaces,such an increase in surface area can increase the adhesion between theadhesive 161 and the piston heads 134A, 134B and thus increase the typesof materials that can be used for the piston heads 134A, 134B.

While the adhesive has been described as being applied in circularregions to the sheet of release paper before cutting the release paperinto a desired shape (e.g., a generally eyeglass shape), in certainimplementations, the adhesive is applied to (e.g., extruded onto) thesheet of release paper in a continuous layer. In such implementations,the adhesive would extend across the entire surface of the releasepaper/adhesive composite that is ultimately produced. In someimplementations, the adhesive is not applied to an edge region of thesheet of release paper such that pull tabs of the release paper/adhesivecomposite can be cut from the edge region to facilitate removal of therelease paper from the adhesive.

In certain cases, ready-to-use adhesive/release paper composites can bepurchased from a supplier. In such cases, the release paper on one sideof the adhesive would be removed from the composite and the exposedadhesive (with the other release paper secured to its opposite side)would be attached to the cassette membrane.

In some implementations, multiple layers of adhesive are used toreleasably attach the piston heads 134A, 134B to the membrane 140. Forexample, as shown in FIG. 19, a double-sided tape 500 is disposedbetween the piston heads 134A, 134B and the membrane 140. For improvedclarity of the cassette, no components of the PD cycler 102 other thanthe piston head 134A and its related piston shaft are shown in FIG. 19.The double-sided tape 500 includes a first adhesive layer 502 and asecond adhesive layer 504 disposed on opposite sides of a base 506. Thefirst adhesive layer 502 is affixed to portions 162A, 162B of themembrane 140 overlying the pump chambers 138A, 138B of the cassette 112.With the first adhesive layer 502 adhered to the membrane 140, thesecond adhesive layer 504 is exposed toward the piston heads 134A, 134B.During use, the piston heads 134A, 134B can be moved into contact withthe second adhesive layer 504 to adhere the second adhesive layer 504 tothe piston heads 134A, 134B. The first adhesive layer 502 in contactwith the membrane 140 can be formed of a biocompatible adhesive toreduce the likelihood of contaminating the PD solution contained in thecassette 112. The second adhesive layer 504 in contact with the pistonheads 134A, 134B can be formed of either a biocompatible orbioincompatible adhesive capable of achieving the desired adhesion tothe material of the piston heads 134A, 134B. In implementations in whichthe first adhesive layer 502 is formed of a biocompatible adhesive andthe second adhesive layer 504 is formed of a bioincompatible adhesive,the base 506 can be formed of low density polyethylene (LDPE). The LDPEbase 506 can resist permeation of the bioincompatible adhesive of thesecond layer 504 and, thus, reduce the likelihood of contamination ofthe biocompatible adhesive in contact with the membrane 140.

The use of two or more different adhesives allows the cassette to beused with membrane/piston head material combinations different thanthose discussed above. For example, multiple different adhesivecombinations can be used for different dialysis systems.

While double-sided tape 500 has been described as including a base 96,the two different adhesives can be directly adhered to one another,particularly if each adhesive is biocompatible.

While the adhesive has been described as being uniformly distributedacross those regions 162A, 162B of the cassette membrane 140 thatoverlie the pump chambers 138A, 138B, other arrangements are possible.For example, in some implementations, the adhesive 161 is distributedover the regions 162A, 162B in a pattern.

While the piston heads 134A, 134B have been described as being axiallymoved to break the attachment between the adhesive and the piston heads134A, 134B, other types of movements of the piston heads 134A, 134B canalternatively or additionally be used to break the attachment betweenthe adhesive and the piston heads 134A, 134B. In some implementations,each piston head is at least partially rotatable about an axisperpendicular to a membrane to detach the piston head from the adhesivethrough a substantially shear force. In certain implementations, eachpiston head is moveable in a direction substantially parallel to themembrane to detach the piston head from the adhesive through asubstantially shear force. By allowing the release of the piston headusing a different type of force than the one used to move the membrane,the likelihood of inadvertent detachment of the piston head can bereduced.

While the piston heads 134A, 134B have been described as being moved(e.g., retracted, rotated, and/or laterally displaced) by a distancesufficient to completely detach the piston heads 134A, 134B from theadhesive, the piston heads 134A, 134B can alternatively be moved by adistance that causes the piston heads 134A, 134B to only partiallydetach from the adhesive. In such implementations, the user can completethe detachment of the piston heads 134A, 134B from the adhesive when theuser pulls the cassette out of the cassette enclosure of the PD cycler.

While the adhesive has been described as being exposed through theremoval of a release paper, other methods of exposing the adhesive arepossible. For example, the adhesive can be formed on the cassette 112through the chemical reaction of two materials on the cassette 112. Insuch a configuration, a first non-adhesive material can be initiallydisposed on regions 162A, 162B of the cassette 112, and a secondmaterial can be placed into contact with the first material to form anadhesive.

While the cassette 112 has been described as being positioned betweenthe locating pins 148 and the lower ledge 150 extending from thecassette interface 110 in order to hold the cassette 112 in a positionsuch that the piston heads 134A, 134B align with the pump chambers 138A,138B, other techniques for ensuring that the piston heads 134A, 134Balign with the pump chambers 138A, 138B can alternatively oradditionally be used. In some implementations, for example, the cassette112 is placed against the door 108 of the PD cycler 102 with thehemispherical projections 154A, 154B of the cassette 112 disposed in therecesses 152A, 152B of the door 108. The cassette 112 is held in thisposition by retainer clips attached to the door 108. Upon closing thedoor 108, the piston heads 134A, 134B of the PD cycler 102 align withthe pump chambers 138A, 138B of the cassette 112. This technique helpsto prevent the adhesive 161 from inadvertently sticking to the pistonheads 134A, 134B or the cassette interface 110 when loading the cassette112 into the PD cycler 102.

While the PD cycler 102 has been described as including a touch screenand associated buttons, the PD cycler can include other types of screensand user data entry systems. In certain implementations, for example,the cycler includes a display screen with buttons (e.g., feathertouchbuttons) arranged on the console adjacent the display screen. Certainbuttons can be arranged to be aligned with operational options displayedon the screen during use such that the user can select a desiredoperational option by pressing the button aligned with that operationaloption. Additional buttons in the form of arrow buttons can also beprovided to allow the user to navigate through the various displayscreens and/or the various items displayed on a particular screen. Otherbuttons can be in the form of a numerical keypad to allow the user toinput numerical values in order, for example, to input operationalparameters. A select or enter button can also be provided to allow theuser to select an operational option to which the user navigated byusing the arrow keys and/or to allow the user to enter values that theuser inputted using the numerical keypad.

While the adhesive laden cassettes described above have been describedas being part of a PD system, these types of cassettes can be used inany of various other types of cassette-based medical fluid pumpingsystems, including hemodialysis systems.

What is claimed is:
 1. A medical fluid delivery cassette, comprising: abase defining an opening; a membrane attached to the base covering theopening, the membrane together with the base defining a fluid pumpchamber, a flow pathway that leads from the fluid pump chamber to aninlet of the cassette, and a flow pathway that leads from the fluid pumpchamber to an outlet of the cassette, and a portion of the membraneoverlying the fluid pump chamber being moveable relative to the basesuch that the volume of the fluid pump chamber can be changed byapplying a force to the portion of the membrane overlying the fluid pumpchamber; an adhesive coating on an outside surface of the portion of themembrane overlying the fluid pump chamber; and a release layersubstantially covering and releasably attached to the adhesive coating.2. The medical fluid delivery cassette of claim 1, wherein the releasepaper is a wax-coated paper.
 3. The medical fluid delivery cassette ofclaim 1, wherein the adhesive coating is disposed on a portion of themembrane that is contacted by a piston head of a medical fluid pumpsystem during use.
 4. The medical fluid delivery cassette of claim 1,wherein the release layer is removable from the adhesive coating toexpose at least a portion of the adhesive coating.
 5. The medical fluiddelivery cassette of claim 4, wherein the release layer comprises a pulltab that extends beyond an outer boundary of the adhesive.
 6. Themedical fluid delivery cassette of claim 1, wherein the medical fluiddelivery cassette is configured for use with a dialysis machine.
 7. Themedical fluid delivery cassette of claim 1, wherein the medical fluiddelivery cassette is configured for use with a peritoneal dialysismachine.
 8. The medical fluid delivery cassette of claim 1, wherein theadhesive coating has a greater affinity for the membrane than for apiston head of a medical fluid pumping system when the cassette is inuse with the medical fluid pumping system such that the piston head canbe retracted in a manner to separate the piston head from the adhesivewithout separating the adhesive from the membrane.
 9. The medical fluiddelivery cassette of claim 1, wherein the adhesive coating comprisesfirst and second layers of adhesive, the first layer of adhesive beingin contact with the membrane.
 10. The medical fluid delivery cassette ofclaim 9, further comprising a base layer disposed between the first andsecond layers of adhesive.
 11. A medical fluid delivery method,comprising: adhering a first piston head of a medical system to amembrane of a medical fluid delivery cassette by moving the first pistonhead into contact with adhesive disposed on a portion the membraneoverlying a first fluid pump chamber; and with the first piston headadhered to the membrane, changing a volume of the first fluid pumpchamber by flexing the portion of the membrane overlying the first fluidpump chamber with the first piston head.
 12. The medical fluid deliverymethod of claim 11, wherein the adhesive has a greater affinity for themembrane than for the first piston head such that the first piston headcan be retracted in a manner to separate the first piston head from theadhesive without separating the adhesive from the membrane.
 13. Themedical fluid delivery method of claim 12, wherein flexing the portionof the membrane overlying the first fluid pump chamber comprises movingthe first piston head away from the cassette with a force that does notexceed the affinity between the membrane and the adhesive.
 14. Themedical fluid delivery method of claim 11, further comprising decouplingthe first piston head from the membrane by moving the first piston headrelative to the cassette.
 15. The medical fluid delivery method of claim14, wherein the adhesive remains attached to the membrane afterdecoupling the first piston head from the membrane.
 16. The medicalfluid delivery method of claim 11, further comprising decoupling thefirst piston head from the membrane by moving the piston head in adirection substantially perpendicular to the cassette.
 17. The medicalfluid delivery method of claim 11, further comprising adhering a secondpiston head to the membrane by moving the second piston head intocontact with adhesive disposed on a portion of the membrane overlying asecond fluid pump chamber and, with the second piston head adhered tothe membrane, changing a volume of the second fluid pump chamber byflexing the portion of the membrane overlying the second fluid pumpchamber with the second piston head.
 18. The medical fluid deliverymethod of claim 11, further comprising disposing the adhesive on themembrane by applying a release layer carrying adhesive to the membrane.19. The medical fluid delivery method of claim 18, further comprisingremoving the release layer from the adhesive.
 20. The medical fluiddelivery method of claim 19, wherein removing the release layercomprises pulling on a pull tab of the release paper, the pull tabextending beyond an outer boundary of the adhesive prior to removing therelease layer from the adhesive.